Magnetic resonance imaging studies of the behavior of fluids in gelatin and other porous materials

Author:

Antalek, Brian J.

Abstract:

An application of magnetic resonance imaging to the study of the diffusion of water
in gelatin and other materials is described. Gelatin was studied in great detail while
plaster, balsa wood, and cement were studied to a lesser degree. Images of the materials at
various stages of the diffusion process were recorded and analyzed. In order to properly
interpret the imaging signal, the relationships between two intrinsic system parameters, Ti
and T2, with the experimental parameters of the study need to be established. In the case
of gelatin studies, Ti and T2 times were measured for gelatin samples varying in gelatin
concentration and degree of D20 dilution. Tx and T2 were found to decrease with
increasing gelatin concentration and increase with increasing D 20 dilution. T 1
relationships were modeled successfully with the crossrelaxation theory while T2
relationships were established empirically. Two gelatin studies were performed, one
involving the counterdiffusion of H20 and D20 in a crosslinked gelatin matrix of a given
gelatin concentration, and one involving the drying of a water containing gelatin matrix.
In the counter-diffusion study, the selfdiffusion coefficient for H20 was found to be 2.0 x
10~5 cm2/s. The diffusion coefficients of H20 in gelatin matricies of 1.5, 5, and 11% wt.
gelatin were found to be 2.0, 1.8, and 1.5 x 10-5 cm2/s, respectfully. In the drying study, it
was found that a good first approximation for the modeling of the drying process is
provided by Fick's second equation solved with a diffusion coefficient depending linearly
with gelatin concentration. The shrinking character of the drying gelatin sample needs to
be included in a more precise model.